What is the most sophisticated AI ever made?
In my opinion, this would be Phaeaco, which was developed by Harry Foundalis at Douglas Hofstadter's CRCC research group.

It takes noisy photographic images of Bongard problems as input and (using a variant of Hofstadter's 'Fluid Concepts' architecture) successfully deduces the required rule in many cases.

Hofstadter has described the related success of CopyCat as being 'like a little kid doing a somersault': i.e. it doesn't have the flashy appeal of systems like AlphaGo. What it does however have is a much more flexible (i.e. not precanned) approach to perception of problem structure than other systems, which Hofstadter claims (and many including Peter Norvig agree) is the really hard problem.